The exes, who ended their marriage in 2015 after 10 years, have remained close in part due to the three children they share, Violet, 16, Seraphina, 13, and Samuel, 10, but according to an insider, it is also because the 13 Going on 30 actress can't let go of the Argo actor.
"Jen will always keep an eye on how Ben's doing," claimed the source, and Affleck continuing to make headlines because of his publicized relationship with Jennifer Lopez isn't helping Garner's concern.
"[Ben] clearly has a lot going on right now with Jennifer and all the attention that comes with their relationship, along with his demanding career, and of course, his kids," added the source of the couple, who had a surprise wedding in Las Vegas last month. "He's being pulled in a lot of directions — and that's something that quietly worries Jen."
Nevertheless, "Jen is happy for Ben," emphasized the source, "that's not what this is about," as Garner has no problem with her ex's new wife.
In fact, "both Jennifers get along very well," another source promised, and the mutual respect between the A-list woman, "has helped positive relations." (Lopez's 14-year-old twins with ex-husband Marc Anthony, Esme and Max, also "get along beautifully" with Lopez and Affleck's kiddos, claimed the source.)
Affleck and Lopez were engaged in 2002 but called off their 2003 nuptials because of the media frenzy surrounding the special day, with the two going their separate way months later. The lovebirds reconciled last year shortly after Lopez called off her engagement to Alex Rodriguez.
In addition to the pressure of being in such a public romance, the 49-year-old has struggled with alcohol addiction in the past, with his third and most recent rehab stint being in 2018.
As Garner continues living her laid-back life with boyfriend John Miller, she remains fearful that history may repeat itself for her burned-out ex, as Affleck juggling so many things at once could push him over the edge.
Affleck and Lopez recently enjoyed a lavish Parisian mini-honeymoon with their blended brood, and while they were seen smiling and walking the streets looking as in love as ever, the actor was also seen breaking down at dinner with his new wife and napping on a boat ride instead of taking in the sights.
"Ben fell asleep because he was exhausted," pointed out the source. "He's been tearing around Vegas and finalizing the purchase of their new home in L.A. His life is a whirlwind."
Referring to the rekindled couple's emotional night at La Griafe restaurant for J.Lo's 53 birthday, the source added, "He's burning the candle at both ends and that's why he got emotional at dinner with Jennifer."
Us Weekly first reported on Garner's concern.